(1) Field of the Invention
The present invention relates to a method for drawing up a special crude oil such as a crude oil containing a large amount of wax or a high-viscosity crude oil.
(2) Description of the Prior Art
A conventional drawing means for a special crude oil will be described in reference to FIG. 3 attached hereto.
A special crude oil is drawn up from an oil well through a pipe line 3 by means of an oil drawing system composed of a casing 5 and a tubing 6. In this case, the special crude oil loses its fluidity, as it is lifted from an oil layer 4 and as its temperature thus falls, so that there occurs the problem that the tubing 6 is clogged thereby. For the prevention of clogging, while the crude oil is drawn up, a crude gas oil is injected into the oil well through a line 2, or alternatively the clogged materials are removed therefrom mechanically.
Heretofore, in drawing up the special crude oil, the crude gas oil is injected thereinto for the purpose of lowering its pour point, and in such a way, there is the problem that the crude gas oil is not always available and cannot be fed thereto on occasion.
The present invention intends to provide a method for drawing up the special crude oil by which the above mentioned problem can be solved.